Reference is made to commonly assigned, co-pending U.S. patent application Ser. No. [Attorney Docket No. 82,453/MSS] entitled A METHOD AND SYSTEM FOR PROCESSING OF PHOTOGRAPHIC MATERIALS by Christopher B. Rider et al., filed concurrently herewith.
The present invention relates to a method and system for calculating the fractional exposure of photographic material. The invention also relates to a method of controlling chemical replenishment and determination of a suitable rate of replenishment to be used in photographic processing.
During the developer stage of photographic processing, a developing agent is used to reduce silver grains that contain a latent image to metallic silver in the emulsion layer of a photographic material being processed. The developer solution is therefore used at a rate that depends upon the image area or exposure of the processed film. The development reaction also results in the creation of unwanted by-products.
The quality of the final image exposed onto the film is critically dependent upon the state or activity of the developer solution. It is therefore important not only to replenish the developer solution to replace the developing agent and flush out the by-products, but also to achieve the correct level of replenishment for the film processed. The developer needs to be replenished at a rate based upon the amount of regeneration required. Therefore the rate of replenishment needs to reflect the amount of developed silver.
Developer solutions are also prone to aerial oxidation and an appropriate addition to the rate of replenishment needs to be made based upon the amount of time the solution has been left idle and exposed to air between processed film areas.
While most processors replenish the developer to account for both aerial oxidation and the area of film processed, usually the film exposure is not known. A user must therefore correctly set the appropriate replenishment rate for the expected average exposure of their processed film according to the manufacturer""s recommendations. In practice, the film manufacturer would be likely to have a recommendation for operation at, say, three levels of exposure covering the likely range over which the film is used. The user selects and applies the developer replenishment rate most appropriate to their particular situation.
In some instances and for some developer and replenisher combinations, solution activity can be maintained by supplying a very high rate of replenishment so that the tank solution contains low levels of development by-products. However, for some replenisher solutions, over-replenishment can be equally detrimental to image quality leading to over-activity. Furthermore, cost and environmental impacts lead a drive to using the minimum required replenishment rate. High activity solutions have even been specifically designed as replenishers for low replenishment rate usage and therefore make the correct choice of replenishment rate settings critical.
A solution to this problem is to replenish the developer such that a first part of the volume of replenisher supplied compensates for changes in activity due to time-dependent processes, such as aerial oxidation and a second part compensates for changes due to development processes.
In the graphic arts industry where high-contrast black and white images are produced, it is known that replenishment rate can be linked to the total amount of black area on developed images to provide effective control of developer activity. The black area is a direct result of the exposure given to the film during the creation of an image on the film and this process of controlling developer replenishment according to the exposure given to the film is known as exposure dependent replenishment (EDR). To use EDR, the fractional exposure of a film being processed is required. In a high contrast material, this is equivalent to the fractional area of the material fully exposed to light, or more generally it is the fraction of the mass of silver ions developed to silver metal.
A number of methods to determine the exposure given to a photographic material so that EDR can be used to control the developer activity and replenishment rate have been proposed. For example, in imagesetting systems, where a direct link exists between the processor and the imagesetter, information such as the integrated total exposure, is transmitted from the imagesetter to the processor and used to control the developer replenishment rate. An example of such a system is described in, for example, United Kingdom Patent Number GB 2,111,726A. A disadvantage of this approach is that custom software must be developed for every different exposing device to which the processor may be connected. This is also clearly of no use to an off-line processor i.e., a processor that is not linked to an exposing device.
Another approach used in the graphic arts industry to obtain exposure information for EDR is to use a post-process scanner to measure the black area on the film. This technique is disclosed in, for example, U.S. Pat. No. 4,314,753 in the name of Pako Corporation. This approach however suffers from the extra cost needed to build a film scanner onto the processor drier. If a high degree of measurement accuracy is required, the extra cost can be substantial.
If the fractional exposure of a film is not supplied or cannot be measured, an alternative method is to directly measure and maintain the developer activity, for example by electrochemical methods. This technique is disclosed in, for example, U.S. Pat. No. 3,970,475. There are drawbacks to these methods since electrochemical sensors require calibration and are prone to drift or fouling. In addition, titration methods to provide and control the required amount of replenisher are difficult to automate into a replenishment system.
Another approach used in the graphic arts industry to obtain exposure information for EDR is to perform a mass balance for the silver entering the fixing stage. This technique is disclosed in, for example, U.S. Pat. No. 3,828,172 in the name of Schickler et al. It relies on the principle that if all the silver that has entered the fixing stage of the processor can be accounted for and if the original total silver content of the processed film is known then the discrepancy in these two figures can be attributed to image area. However, a problem with the technique disclosed in U.S. Pat. No. 3,828,172 is that the use of a silver ion sensor is required to determine the total silver content of the fixing stage, which is one of the key terms in the calculation discussed therein. Thus, the apparatus required to operate the method described is expensive in that a silver sensor must be supplied and kept calibrated in customer usage. In addition, the silver sensor introduces problems of robustness, drift, accuracy and calibration to the determination of the fixing stage silver content and/or silver concentration.
Problem to be Solved by the Invention
A method of and a system for calculating the fractional exposure of photographic material and a corresponding rate of replenishment to be used in photographic processing is required that overcomes all the problems described above. In particular, a method and system of photographic processing is required that overcomes all the previously mentioned disadvantages, providing a method requiring minimal additional cost and sufficient accuracy.
According to a first aspect of the present invention, there is provided a method of calculating the fractional exposure of photographic material. The exposed material is processed in a processing system having a developing stage, a fixing stage and an in-line silver recovery unit associated with the fixing stage. The process comprises determining the mass of silver recovered by the in-line silver recovery unit during a period of operation of the method; calculating a first estimate for the fractional exposure of the photographic material in dependence on the determined mass of silver; and using the first estimate as an input to an iterative process to obtain a subsequent estimate for the fractional exposure (xcex8) of the photographic material.
Preferably, the iterative process comprises the steps of calculating an estimate for the silver leaving the fixing stage in processing fluid during the period of operation in dependence on the last calculated estimate for the fractional exposure; and calculating a subsequent estimate for the fractional exposure of the photographic material using the estimate obtained for the silver leaving the fixing stage in processing fluid in the estimate calculation step.
Preferably, the first estimate for the fractional exposure of the photographic material is obtained by using the following equation:       1    -    θ    ≈      (                  A        ⁢                  xe2x80x83                ⁢                  g                      R            ⁢                          xe2x80x83                        ⁢            E            ⁢                          xe2x80x83                        ⁢            C                                      ∑                  A          ⁢                      xe2x80x83                    ⁢          r          ⁢                      xe2x80x83                    ⁢          e          ⁢                      xe2x80x83                    ⁢          a          xc3x97          C          ⁢                      xe2x80x83                    ⁢          o          ⁢                      xe2x80x83                    ⁢          a          ⁢                      xe2x80x83                    ⁢          t          ⁢                      xe2x80x83                    ⁢          e          ⁢                      xe2x80x83                    ⁢          d          ⁢                      xe2x80x83                    ⁢          W          ⁢                      xe2x80x83                    ⁢          e          ⁢                      xe2x80x83                    ⁢          i          ⁢                      xe2x80x83                    ⁢          g          ⁢                      xe2x80x83                    ⁢          h          ⁢                      xe2x80x83                    ⁢          t                      )  
in which, AgREC is the mass of silver recovered during the period of operation;
Area is the area of each piece of photographic material processed during the period of operation; and Coated Weight is the mass of silver per unit area in each piece of photographic material processed during the period of operation.
Preferably, the subsequent estimate for the fractional exposure of the photographic material is obtained by using the following equation:       1    -    θ    =      (                  (                              A            ⁢                          xe2x80x83                        ⁢                                          g                                  E                  ⁢                                      xe2x80x83                                    ⁢                  FF                                            ⁡                              (                                  1                  +                                                            R                                              C                        /                        O                                                                                                            η                        1                                            ⁢                                              R                                                  F                          ⁢                                                      xe2x80x83                                                    ⁢                          I                          ⁢                                                      xe2x80x83                                                    ⁢                          X                                                                                                                    )                                              +                      A            ⁢                          xe2x80x83                        ⁢                          g                              R                ⁢                                  xe2x80x83                                ⁢                E                ⁢                                  xe2x80x83                                ⁢                C                                                    )                    ∑                  A          ⁢                      xe2x80x83                    ⁢          r          ⁢                      xe2x80x83                    ⁢          e          ⁢                      xe2x80x83                    ⁢          a          xc3x97          C          ⁢                      xe2x80x83                    ⁢          o          ⁢                      xe2x80x83                    ⁢          a          ⁢                      xe2x80x83                    ⁢          t          ⁢                      xe2x80x83                    ⁢          e          ⁢                      xe2x80x83                    ⁢          d          ⁢                      xe2x80x83                    ⁢          W          ⁢                      xe2x80x83                    ⁢          e          ⁢                      xe2x80x83                    ⁢          i          ⁢                      xe2x80x83                    ⁢          g          ⁢                      xe2x80x83                    ⁢          h          ⁢                      xe2x80x83                    ⁢          t                      )  
in which, AgREC is the mass of silver recovered during the period of operation; AgEFF is the mass of silver associated with fixing solution which passes out of the fixing stage other than by carry out with processed material during the period of operation; RFIX is the fixer replenishment rate; RC/O is the rate of carry-out of solution by the processed material from the fixing stage; and xcex71 is an efficiency factor for fixing which is both fixing time and silver concentration dependent. The estimate for the silver lost to effluent during the period of operation is obtained by using the following equation:       A    ⁢          xe2x80x83        ⁢          g              E        ⁢                  xe2x80x83                ⁢        FF              ≈                    V        EFF            2        ⁢          (                        [                      A            ⁢                          xe2x80x83                        ⁢                          g              INITIAL                                ]                +                              (                                                            V                  TANK                                ⁡                                  [                                      A                    ⁢                                          xe2x80x83                                        ⁢                                          g                      INITIAL                                                        ]                                            +                                                θη                  2                                ⁢                                  ∑                                      A                    ⁢                                          xe2x80x83                                        ⁢                    r                    ⁢                                          xe2x80x83                                        ⁢                    e                    ⁢                                          xe2x80x83                                        ⁢                    a                    xc3x97                    C                    ⁢                                          xe2x80x83                                        ⁢                    o                    ⁢                                          xe2x80x83                                        ⁢                    a                    ⁢                                          xe2x80x83                                        ⁢                    t                    ⁢                                          xe2x80x83                                        ⁢                    e                    ⁢                                          xe2x80x83                                        ⁢                    d                    ⁢                                          xe2x80x83                                        ⁢                    W                    ⁢                                          xe2x80x83                                        ⁢                    e                    ⁢                                          xe2x80x83                                        ⁢                    i                    ⁢                                          xe2x80x83                                        ⁢                    g                    ⁢                                          xe2x80x83                                        ⁢                    h                    ⁢                                          xe2x80x83                                        ⁢                    t                                                              -                              A                ⁢                                  xe2x80x83                                ⁢                                  g                                      P                    ⁢                                          xe2x80x83                                        ⁢                    R                    ⁢                                          xe2x80x83                                        ⁢                    O                    ⁢                                          xe2x80x83                                        ⁢                    C                                                                        )                                              V                              T                ⁢                                  xe2x80x83                                ⁢                A                ⁢                                  xe2x80x83                                ⁢                NK                                      +                          V              EFF                                          )      
in which, VEFF is the volume of fixer effluent generated; VTANK is the volume of the fixing stage including the silver recovery unit; [AgINITIAL] is the silver concentration of the fixing stage including the silver recovery unit at the start of the period of operation; AgPROC is the mass of silver removed in the time between the end of processing of a first area of photographic material and the start of processing of a final area of photographic material during the period of operation; and xcex72 is an efficiency factor for fixing which is both fixing time and silver concentration dependent.
According to a second aspect of the present invention, there is provided a method of control for use in a photographic processing system having processing stages including a developing stage, a fixing stage and an in-line silver recovery unit associated with the fixing stage. The steps of the method include: calculating the fractional exposure of the photographic material in accordance with the method of the first aspect of the present invention; and using an exposure-dependent algorithm to determine an appropriate replenishment rate for at least one of the processing stages in dependence on the calculated fractional exposure.
According to a third aspect of the present invention, there is provided a photographic processing system, comprising a fixing stage to receive and fix developed black and white photographic material; an in-line silver recovery unit associated with the fixing stage to recover silver from processing solution in the fixing stage; and control means to determine the mass of silver recovered by the in-line silver recovery unit and calculate the fractional exposure of the processed photographic material. The control means is arranged to iteratively calculate the fractional exposure of the photographic material in dependence on the determined mass of silver.
Preferably, the system further comprises a developing stage to develop photographic material and provide the material to the fixing stage and a washing stage to receive and wash photographic material from the fixing stage.
Preferably, the control means is arranged to calculate a first estimate for the fractional exposure of the photographic material in dependence on the determined mass of silver;
calculate a corresponding estimate for the mass of silver leaving the fixing stage in processing fluid during a period of operation thereof in dependence on the first estimate for the fractional exposure; and
calculate a subsequent estimate for the fractional exposure of the photographic material using the estimate calculated for the silver leaving the fixing stage in processing fluid.
Advantageous Effect of the Invention
The use of in-line electrolytic silver recovery is known in photographic systems and it enables users to:
i. reduce their fixer replenishment rates;
ii. reduce the total amount of silver passing into the wash tank and hence maintain compliance with local silver discharge codes when passing wash water directly to drain; and
iii. recover valuable silver.
The invention provides a method and system that uses silver recovery units to enable simple calculation of the fractional exposure of photographic material being processed. This in turn enables control of the replenishment rate for the photographic processing system to be achieved. In particular, an iterative process is used to calculate the fractional exposure of photographic material being processed, the only required initially unknown input to the iteration being the recovered mass of silver by the silver recovery unit. Accordingly, there is no need for any complex ion sensors to determine the silver concentration of processing solution in the fixing stage (as required for example in Schickler et al). Therefore the problems of the cost of the ion sensors and the need to calibrate them are overcome.
In addition, the cost of purchasing silver recovery units is soon recovered through the cost savings achieved by recycling the recovered silver. The present invention uses information, which can be obtained from the operation of the silver recovery unit and the processing system to determine the amount of developed silver in the images and so provide the information which is necessary for control of the developer activity by EDR.